I think we saw it to be smaller than 725 meters. I don't know what you mean by the idea if being 725 meters. I'll state a couple of examples, the escape ejection scene, the nibiru scene, the shuttle entering Enterprise landing bay in STID and the vengeance crash scene. I'll focus on the two STID scenes, we see the shuttle entering the shuttlebay and it's right there next to the opening structure of the bay, shadows and all. The ship looks a lot smaller than 725 there, the Vengeance crash also shows a Vegeance that's clearly not almost a mile long. Alcatraz is approximately 1 mile away from the waterfront and the Vengeance easily fits into that gap with ample room when it hits the water. Like Daniel's sig, that doesn't show everything but that's the scene I'm talking about

And here's the entire Vengeance crash sequence in HD, courtesy of Paramount France.

Back when the film opened, Locutus of Bored posted a cool map showing Vengeance's path of destruction, and it's relative size to Alcatraz Island at what we'd guesstimated at the time to be 1450m/4757ft - extremely close to ILM's 4500ft and Qmx's 4800ft figures. I'll see if I can find it.

I drew the path in google earth from the lighthouse to the waterfront size the island itself is angled and got a 6,382 foot path, the ship would fill more than half of that space if it were 4500 feet long and in the scene it didn't fill more than half. Can you provide the image showing the shuttle itself inside the mouth of that bay in the same image?